html,body{
  width: 100%;height: 100%;overflow: hidden;padding: 0;
  margin: 0;
}
#root{width: 100%;height: 100%; display: flex; flex-direction: column;align-items: center;}

#header {
  width: 100%;
  height: auto;
  flex-shrink: 0;
}
#main {
  width: 100%;
  flex: 1;// flex 1的意思就是 flex-grow 1,这里是缩写
  // flex-grow: 1;
  overflow-y: auto;
}

